Next week, Mitt Romney's campaign seeks to introduce Paul Ryan again. Even before the selection of the Republican vice presidential choice, President Obama's campaign had been working to define Ryan as extreme on issues from Medicare to abortion. What happens next week is that Romney and Ryan take the stage at the Republican National Convention, one of several things that will happen there.

Cokie Roberts is here to talk about that and more. Cokie, good morning.

COKIE ROBERTS, BYLINE: Hi, Steve.

INSKEEP: She joins us most Mondays. Now these conventions sometimes showcase divisions within the parties, but nobody seems to expect that this time around.

ROBERTS: No, that's right. And, you know, I started covering Republican platform hearings back in 1980 when they could be very contentious on all kinds of issues. But the parties have become much more unified and polarized. So that back then - when the platform was, you know, getting people upset on issues like abortion and then following that on taxes - you had 42 percent of Republicans identifying themselves as conservatives. Now, 63 percent say that they are conservatives.

So it's much more conservative party and a much more unified party. And, by the way, on the Democratic side, similar kinds of numbers. Back then 21 percent called themselves liberals. Now it's 38 percent. And back then, a bunch of Democrats, a third, said they were conservatives - no more.

INSKEEP: Well, Democrats were demonstrably divided on the issue of gay marriage just a few years ago. But it appears they're going to adopt a party platform that includes endorsing the legalization of gay marriage this time around.

ROBERTS: And I think that they have decided, partly, that that is a way to energize people in their base, which includes not only gay people, but young people who are very liberal on the subject of gay marriage. But it's also true that the Democrats feel that any downside on this issue is already attached to them; that they, you know, anybody who's going to vote on the issue of gay marriage is going to vote against the Democrats anyway.

But it is interesting, because they don't think that independents are as important as one would think that they would think they are, given the fact that more and more voters identify themselves as independents. And then, now, it's the plurality of voters in some polls. And the president has a big independent problem but that doesn't seem to be focus of these campaigns.

INSKEEP: Don't seem to be a lot of independent voters out there, undecided voters anyway.

ROBERTS: I know and pollsters keep trying to explain to me why, with the huge number of independents we have, the undecided vote is so low. And one of the answers they say is, well, look. At any given moment when you ask the question: Who are you voting for, for president, people will decide an answer. But those people can be swayed. And they can be swayed, both by events and by what happens in a political campaign.

Take for instance what happened yesterday in the Missouri Senate race. There, the Democratic incumbent, Claire McCaskill, has been running behind her Republican challenger, Todd Akin. But he said yesterday in an interview, when asked about his views on abortion, that victims of, quote, "legitimate rape rarely get pregnant," that the female body, quote, "has ways to try to shut that whole thing down."

Well, as you can imagine, McCaskill has jumped all over that. Romney and Ryan have distanced themselves from that. But those kinds of comments can make a tremendous difference in the campaign. I wouldn't expect that kind of thing at the presidential level, but we'll watch and see.

INSKEEP: Yeah, Akin has said he misspoke but a lot of prognosticators are saying the damage is done there.